The Natural Mutation Encoding a C Terminus-Truncated 5-Hydroxytryptamine2B Receptor Is a Gain of Proliferative Functions

Abstract

Although potentially implicated in several physiological functions, few functional mutations have been identified in the human 5-hydroxytryptamine (HT) 2B receptor gene. A heterozygous mutation R393X in the 5-HT 2B receptor was recently identified in a patient diagnosed with pulmonary hypertension after intake of the anorexigenic dexfenfluramine. Although reported to generate a lack of function, this C terminus-truncated 5-HT 2B receptor should somehow affect transduction pathways relevant to pulmonary hypertension. In our study, we investigated putative modifications in transduction of the R393X-mutated 5-HT 2B receptor. In stably transfected cells, we confirmed the loss of inositol 1,4,5-trisphosphate stimulation caused by the G ␣q uncoupling, despite conserved ligand affinity between the normal and mutated receptors. We also observed a partial loss of nitric-oxide synthase stimulation. However, the truncated R393X receptor presented 1) a strong gain of efficacy in cell proliferation as assessed by mitogen-activated protein kinase activity and thymidine incorporation, 2) a preferential coupling to G ␣13 as shown by blocking antiserum, and 3) an apparent lack of internalization upon agonist stimulation as observed by confocal microscopy. This work demonstrates that, in the 5-HT 2B receptor, the C terminus, including the palmitoylation and phosphorylation sites, is absolutely required for proper transduction and internalization. For the first time, we show that the lack of C terminus can generate a switch of coupling to G ␣13 , a reduced NO synthase activation, and an increase in cell proliferation. All these modifications are relevant in pathophysiological vasoconstriction.Knowledge of 5-HT 2B receptor genetic variants is of the utmost interest in view of the involvement of these receptors in various pathologies (Roth and Shapiro, 2001). Few studies have investigated mutations in the 5-HT 2B receptor gene (MIM 601122). It was identified as a candidate gene in obsessive-compulsive disorder: one single nucleotide polymorphism was described in intron 1, but no evidence for functional mutation was found in the coding regions of 5-HT 2B receptor (Kim et al., 2000). More recently, by investigating the 5-HT 2B receptor gene in patients who developed pulmonary hypertension after intake of fenfluramines, a heterozygous mutation was found in one female who 5 years before followed a 9-month anorexigenic treatment (Blanpain et al., 2003). The reported mutation consists of a C/T transition This work has been supported by funds from the Centre National de la Recherche Scientifique, the Institut National de la Santé et de la Recherche Médicale, the Hôpital Universitaire de Strasbourg, the Université Louis Pasteur, and by grants from the Fondation de France, the Fondation pour la Recherche Médicale, the Association pour la Recherche contre le Cancer, the French ministry of research (Actions Concertées Incitatives), and the European Community.

Exogenous Serotonin Regulates Proliferation of Interstitial Cells of Cajal in Mouse Jejunum Through 5-HT2B Receptors

“…At higher doses, 5-HT had no effect on ICC numbers. This lack of effect at higher concentrations may be due to receptor internalization 59 or desensitization 60 or is possibly due to an effect of 5-HT on other receptors.…”

Modified Receptor Internalization upon Coexpression of 5-HT1BReceptor and 5-HT2BReceptors

“…Despite the coexpression of 5-HT 1B and 5-HT 2B receptors in various tissues including endothelial and smooth muscle cells (Ullmer et al, 1995), and given the inhibitory effect of 5-HT 2B receptors on 5-HT 1B receptor signaling (Tournois et al, 1998), physical interaction between the two receptors seems plausible. The internalization of the 5-HT 2B receptor is faster than that of 5-HT 2A and 5-HT 2C receptors (Porter et al, 2001;Schaerlinger et al, 2003;Deraet et al, 2005), although the mechanism underlying this distinction has not been uncovered. In this work, we investigated potential 5-HT 1B/2B receptor interactions by examining the colocalization and internalization kinetics of 5-HT 1B and 5-HT 2B receptors expressed alone or together.…”

Terguride ameliorates monocrotaline-induced pulmonary hypertension in rats

“…First, a mutation causing premature truncation of 5-HTR 2B was described in a patient with PAH associated with fenfluramine use [46]. Although originally considered a lossof-function mutation, subsequent analysis indicated that this mutation was associated with a complete loss of inositol 1,4,5-trisphosphate and a partial loss of nitric oxide synthase stimulation, with a strong gain of efficacy in cell proliferation [47]. Secondly, acute administration of PRX-08066 resulted in a reduction in systolic pulmonary blood pressure during exercise-induced hypoxia in humans without effect on systemic blood pressure [48].…”